Support arbitary BL for accessor

[zibaiwan]

Tested with a variety of tests group.

[sophimao]

Thanks Zibai! LGTM, just one small nit below that you can make the call whether you want to change it or not :)

[zibaiwan]

I made a minor update here in the auto_configure.cpp

std::string gmem_id = "-"; // This should be the default value even if the // auto-discovery string doesn't have this field.

[sophimao]

Thanks Zibai!